Can I put more than one backup on DDS with fbackup?

No. fbackup always rewinds the tape. Possible alternatives:

(1) Stick with dump/cpio/tar/pax.
(2) Use a pipe: instead of telling fbackup where the DAT is,
let it send its output to stdout (-f -) and pipe it to the DAT,
Berkeley no-rewind device and dd with a suitable block size (e.g.,
10K). You'll lose fast-search and resync-after-error functionality,
though. Also, the complexities of managing multiple archives per
tape make this a high-risk proposition.
(3) Use NFS[R] and mount the disks of the machine without DAT to the
other and back them both up there. You'll have to mount 'em with
root permissions and restoring a completely destroyed root disk will
be messy.
(4) Scream at HP until they fix fbackup. :-)

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